BOTH THE SEXES IN DIPTEEA. 357 



Homology ivifh oripositor. — The sac at the base of the oviduct in the Blow-fly appears 

 to homolog'ize with this part. It is in the passage leading from the sac into the uterus 

 that the ducts from the receptacula seminis discharge, impregnating the ova in their 

 passage. But Lowne regards it as homologous with the uterovaginal tube *, which is 

 after all exceedingly close to the part I suggest. In JIusca domesiica there is a cavity 

 at the end of the passage into which the ductus ejaculatorius discharges, which is possibly 

 also homologous. This is well shown in Berlesi's section already alluded to, but any 

 longitudinal section of the ovipositor in its normal position in the abdomen which shows 

 the receptacula seminis, or spermathecse, will probably show the part I mean. 



(r) The Vas deferens. 



The vas deferens is the tube which leads from the paragonia and testes to the sacculus 

 ejaculatorius. 



Structure. — It is usually a subhyaline membrane with many longitudinal wrinkles. 

 It is of various lengths, short or long in diiferent families. In Dolichopus it has a very 

 marked muscular structure, and broadens out at its junction with the secretory organs. 

 Besides its length, it has little to distinguish it in the various families. 



Homology. — It homologizes with the oviduct of the female. 



(s) The Paragonia or Yesictjl^ seminales. 



These are a pair of sacs which open into the vas deferens. Their function is obscure, 

 but Lowne t rejects the idea that they contain spermatozoa, and considers that in the 

 Blow-fly at least, " the secretion coagulates with great rapidity in the ejaculatory 

 duct or in the vagina of the female insect, and is apparently concerned in the formation 

 of spermatophores." 



Homology. — They are easily homologized with the glands which Lowne calls parovaria 

 in CalUphora, and have been confused with the " glue-glands " +. 



(/) Vasa efferentia. 



These are ducts which lead from the testes to the vas deferens. They are so named 

 by Lowne §, but are the " vasa deferentia " of other writers. These organs are always 

 jiresent, visually of a hyaline structure and of varying length. They homologizc Avitb 

 the " tubse " of Lowne, Avhich lead from the ovaries to the oviduct. 



(m) The Testes. 



These are paired sacs, which secrete the spermatozoa ; are mostly separated, and of 

 an orange, white, or brown colour. Dufour says, however, that in Laphriafulva, Egger, 

 both testes are enveloped in one receptacle, " im veritable scrotum " ||. 



Structure. — In Musca domesiica they are of a deep brown, and have the appearance 



• ' Blow-fly,' p. G75. t ' 131ow-fly,' p. 663. 



% Ibid. p. t)7:{. § Ibiil. p. V)ij2. 



\\ Rechcrchcs anutomiijues, etc. p. 198. 



52* 



